The purpose of this Center is to assist investigators in the U.S.A. and abroad in the identification of arboviruses. To this end the Center maintains a complete collection of virus seeds, antigens and immune sera or ascitic fluids which it uses for its own work as well as distributing them on request to specialized laboratories for specific purposes. During the calendar year 1973, the Center has investigated 137 submitted viruses from its backlog of about 250; of these 12 were identified as apparently new agents and 6 were recognized as new viruses in the area or hosts from which they were isolated. Of particular interest has been the assistance given by the Center in the diagnosis of febrile disease in Nepal, West Africa, and Chile. The goal for the calendar year 1974 is the identification of 80 virus strains including viruses from Panama, Africa, and Asia. New techniques for study of the antigenic, biological, and physicochemical properties of viruses of major human disease potential such as Crimean hemorrhagic fever-Congo, yellow fever, dengue, and Venezuelan encephalitis are being developed and will be stressed.